Assembly comprising a blanket unit and a cylinder having a blanket fixing device, a corresponding cylinder, blanket unit and offset printing machine

ABSTRACT

An assembly for an offset printing machine having a blanket unit comprising a blanket and a blanket support plate, the front edge and rear edge of the support plate being bent over and extending beyond the front edge and rear edge of the blanket, and a cylinder having an aperture for receiving the front edge and rear edge of the support plate, the cylinder comprising a device for fixing the blanket unit to the cylinder, the fixing device comprising at least one hook for tensioning the blanket unit.

TECHNICAL FIELD

The present invention relates to an assembly for an offset printingmachine comprising:

-   -   a blanket unit comprising a blanket and a blanket support plate,        the front edge and rear edge of the support plate being bent        over in the region of a front bend and a rear bend,        respectively, the rear edge of the support plate protruding        beyond the rear edge of the blanket which is located adjacent to        the rear bend, and    -   a cylinder having an aperture for receiving the front edge and        rear edge of the support plate, the cylinder comprising a device        for fixing the blanket unit to the cylinder, the fixing device        comprising at least one hook for tensioning the blanket unit,        the hook being intended to be received in an opening of the rear        edge of the support plate, which rear edge is inserted into the        aperture, in order to apply to the support plate a tension load        which is substantially parallel with the rear edge thereof.

BACKGROUND TO THE INVENTION

A printing machine of this type conventionally comprises, in addition tothe blanket-carrying cylinder and the blanket, a plate-carrying cylinderand a plate and a pressing cylinder.

During operation, the plate carried by the plate-carrying cylinder ismoistened then inked. The plate transfers the ink from the printingregions thereof to the blanket carried by the blanket-carrying cylinder.The blanket then transfers the ink to the paper to be printed whichpasses between the blanket-carrying cylinder and the pressing cylinder.

In order to tension the blanket on the cylinder, metal bars crimped tothe ends of the blanket were traditionally used. These bars were engagedin the aperture of the cylinder, where they were pushed by a screw-typedevice.

Such arrangements lead to aperture widths which are very large, reaching22 mm.

The presence of such large apertures results in shocks and vibrationswhen the blanket-carrying cylinder rotates against the plate-carryingcylinder and against the pressing cylinder. Such vibrations limit therotation speeds of the various cylinders and therefore the productioncapacities of offset printing machines.

FR-2 573 347 proposed an assembly of the above-mentioned type. The frontedge of the blanket covers all the front edge of the support plate andtherefore extends into the cylinder aperture. The rear edge of theblanket does not extend into the aperture and is applied substantiallyagainst the region of the front bend of the blanket unit. In thismanner, the gap between the start of the blanket and the end of theblanket is extremely narrow in order to limit the vibrations whichresult from the presence of the aperture in the cylinder.

However, it was found that it was extremely difficult to bend the frontedge of the plate and the front edge of the blanket in order to obtainthe configuration desired in this document.

FR-2 733 719 proposed another solution in which the device for fixingthe blanket unit comprises pressing studs which apply the front and rearedges of the support plate against the front wall of the aperture. Thesefront and rear edges of the support plate are not covered by theblanket. The forces applied by the studs are exclusively perpendicularto the front and rear edges of the support plate.

It was found that this arrangement did not allow the blanket unit to betensioned satisfactorily. In addition, the fixing device described doesnot allow the deformations of the blanket unit resulting from theoperation of the offset printing machine to be absorbed. In particular,the expansions of the support plate cannot be absorbed so that cracks inthe plate adjacent to the rear bend thereof are observed.

FR-2 745 524 proposed that the pressing studs be replaced with one ormore resilient blades. However, this arrangement does not always allowsatisfactory tension of the blanket unit to be obtained.

An object of the invention is to provide an assembly of theabove-mentioned type which allows the blanket unit to be tensioned onand fixed to the cylinder in a satisfactory manner and which is simpleand economical to produce.

SUMMARY OF THE INVENTION

To this end, the invention relates to an assembly of the above-mentionedtype, characterised in that the front edge of the support plateprotrudes beyond the front edge of the blanket which is located adjacentto the front bend.

According to particular embodiments, the assembly can comprise one ormore of the following features, taken in isolation or according to alltechnically possible combinations:

-   -   the opening is provided in a region of the rear edge of the        support plate forming an angle which is not equal to zero with        the front edge of the support plate,    -   the hook comprises a resilient blade,    -   the assembly comprises means for applying the front edge of the        support plate against the front wall of the aperture, these        application means being separate from the hook,    -   the application means comprise at least one element for pressing        on the front edge of the support plate, the pressing element        belonging to the fixing device and being separate from the        support plate,    -   the pressing element extends, in order to press on the front        edge of the support plate, through the opening which receives        the hook,    -   the pressing element comprises a resilient blade,    -   the rear edge of the support plate is itself bent in the region        of an intermediate bend which delimits an end region, in which        the opening for receiving the hook is provided, and an        intermediate region which is intended to press against the front        edge of the support plate and which thereby forms the        application means,    -   the aperture has a width, near the peripheral surface of the        cylinder, of less than 1.5 mm,    -   the width of the aperture is less than 1.1 mm,    -   the front and rear walls of the aperture form, starting from the        peripheral surface of the cylinder, an angle which is less than        20°.

The invention also relates to a cylinder for an assembly as definedabove.

According to one variant, the fixing device comprises at least oneelement for pressing on the front edge of the support plate in order toapply it against the front wall of the aperture, the pressing elementbeing separate from the hook.

The invention further relates to a blanket unit for an assembly asdefined above.

According to one variant, the rear edge of the support plate is itselfbent in the region of an intermediate bend which delimits an end region,in which the opening for receiving the hook is provided, and anintermediate region which is intended to press against the front edge ofthe support plate in order to apply it against the front wall of theaperture.

The invention also relates to an offset printing machine comprising anassembly as defined above.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be better appreciated from the description belowwhich is given purely by way of example with reference to the appendeddrawings, in which:

FIG. 1 is a schematic side view of an assembly according to a firstembodiment of the invention,

FIG. 2 is a schematic partial cross-section, drawn to an enlarged scale,illustrating the fixing device of the blanket unit of the assembly ofFIG. 1,

FIG. 3 is a schematic partial top view, illustrating part of the spindleof the fixing device of FIG. 2,

FIG. 4 is a schematic partial view illustrating the rear edge of thesupport plate of the blanket unit,

FIGS. 5 and 6 are views similar to FIG. 2, illustrating successive stepsin the engagement of the blanket unit with the fixing device,

FIG. 7 is a view similar to FIG. 1, illustrating the position of a drivemechanism of the fixing device at the end of the fixing of the blanketunit,

FIG. 8 is a view similar to FIG. 6, illustrating a second embodiment ofthe invention and

FIG. 9 is a view similar to FIG. 6, further illustrating a thirdembodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 illustrates schematically an assembly 1 for an offset printingmachine which comprises a cylinder 2 and a blanket unit 3 whichsurrounds the peripheral surface 4 of the cylinder 2 and which iscarried by the cylinder 2.

The cylinder 2 extends along a longitudinal axis A and the longitudinalends 5 thereof, only one of which is visible in FIG. 1, are intended tobe received in bearings of the support structure of an offset printingmachine. In this manner, the cylinder 2 can, owing to conventionaldriving means which are not illustrated, rotate about the longitudinalaxis A thereof in a sense illustrated by the arrow 6 in FIG. 1.

Hereinafter, the terms “front” and “rear” used should be understood withreference to this sense of rotation 6.

As is visible in FIG. 2, a longitudinal recess 8 has been provided inthe cylinder 2 from the peripheral surface 4 thereof. This recess 8 issubstantially in the form of a regular trapezium in cross-section withone rounded side corresponding to a portion of the peripheral surface 4of the cylinder 2.

An insert 10 is screwed into the recess 8.

This insert 10 delimits inside the cylinder 2 a longitudinal cavity 12having a substantially rectangular cross-section and a longitudinalaperture 14 having a substantially triangular cross-section.

The aperture 14 opens into the peripheral surface 4 of the cylinder 2and into the cavity 12.

As illustrated in greater detail by the enlarged circled portion of FIG.2, the front wall 16, which is common to the aperture 14 and the cavity12, is connected to the peripheral surface 4 by a chamfer 18, forexample, having a width of approximately 1 mm.

Similarly, the rear wall 20 of the aperture 14 is connected by a chamfer22 to the peripheral surface 4. This chamfer 22 has, for example, awidth of approximately 1.4 mm.

The front wall 16 and rear wall 20 of the aperture 14 diverge as theyapproach the cavity 12, that is to say, from an upstream point towards adownstream point of the aperture 14. The walls 16 and 20 thus formbetween them an angle α which is typically approximately 14.8°. Moregenerally, this angle a will be less than 20°.

The upstream width 1 of the aperture 14 between the walls 16 and 20,that is to say, downstream of the chamfers 18 and 22 is approximately 1mm. More generally, this width 1 will be less than 1.5 mm, andpreferably less than 1.1 mm.

The cylinder 2 comprises a device 26 for fixing the blanket unit 3 tothe cylinder 2. This device 26 is arranged in the cavity 12 andcomprises a spindle 28 which extends along an axis X—X which issubstantially parallel with axis A of the cylinder 2. This spindle 28extends, for example, all the way along the cylinder 2.

As illustrated by FIGS. 2 and 3, hooks 30 and pressing elements 32 aredistributed along the spindle 28.

The hooks 30 are formed by resilient blades whose free ends 34 arecurved opposite the aperture 14.

Similarly, the pressing elements 32 are formed by resilient blades whosefree ends 36 are bent through 180°.

The hooks 30 and the pressing elements 32 are associated in pairs, theassociated hook 30 and pressing element 32 being fixed to the spindle 28by a common screw 38. The pressing element 32 is arranged above theassociated hook 30.

The pairs comprising a hook 30 and pressing element 32 are spaced apartfrom each other longitudinally and distributed along the spindle 28.

The spindle 28 is mounted so as to be able to rotate about longitudinalaxis X—X thereof in the cavity 12 owing to, for example, bearingsprovided at the ends of the spindle 28 and optionally in intermediateregions thereof.

In this manner, the spindle 28 can move between two positionsillustrated by FIGS. 2 and 6, respectively.

In the position of FIG. 2, or the release position of the blanket unit3, the hooks 30 and the pressing elements 32 are moved away from theaperture 14 and free up the access to the cavity 12.

In the position of FIG. 6 or the fixing position of the blanket unit 3,the hooks 30 and the pressing elements 32 are moved towards the frontwall 16.

In order to move from the position of FIG. 2 into the position of FIG.6, the spindle 28 pivots in the counter-clockwise sense, as seen inthese Figures. This pivoting can be brought about by drive mechanisms42, only one of which is visible in FIG. 1, the other having a similarstructure and being arranged at the other side of the cylinder 2. Thus,only the mechanism 42 visible in FIG. 1 will be described below.

The drive mechanism 42 can comprise, for example:

-   -   a support 44 fixed to a flank of the cylinder,    -   a rod 46 which is provided with a collar 48 and which is        surrounded by a spring 50,    -   a block 52 which is fixed to the corresponding longitudinal end        54 of the spindle 28, and    -   a moveable operating lever 56, which is illustrated as a        dot-dash line in FIG. 1.

The rod 46 is articulated to the block 52 at a first end thereof. Therod 46 is mounted, at the other end thereof, in the support 44 by meansof an articulation which allows it to pivot in a plane at right-anglesto axis A of the cylinder 2. The spring 50 presses, on the one hand, onthe block 44 and, on the other, on the collar 48.

Owing to the lever 56, the rod 46 can move relative to the support 44between two stable end positions.

The first stable end position is illustrated in FIG. 1, This positioncorresponds to the release position of the spindle 28, illustrated inFIG. 2.

The second stable end position is illustrated in FIG. 7. In thisposition, the spindle 28 is in the fixing position illustrated in FIG.6.

In order to move from the position in FIG. 1 to that in FIG. 7, anoperator pivots the lever 56 in the counter-clockwise sense, asillustrated by the arrow 60 in FIG. 1.

The rod 46 will then move through an unstable neutral position, wherethe axis thereof will intersect with axis X—X of the spindle 28. Thespring 50 is then compressed so that it will return the rod 46 towardsthe second stable position thereof, that is to say, the position of FIG.7. The block 52 is then pressed against an adjustable stop 58 whichallows the angular position of the spindle 28 in the fixing positionthereof to be adjusted.

In this manner, the mechanism 42 for passing through the neutralposition allows the spindle 28 to be displaced manually from the releaseposition thereof towards the fixing position thereof, and vice versa.However, it should be noted that any other type of drive mechanism 42can be used.

With reference once more to FIG. 2 it will be appreciated that theblanket unit 3 comprises a support plate 62 and a blanket 64 which isfixed to the support plate 62.

The support plate 62 is produced, for example, from stainless steel. Itsthickness is approximately 0.2 mm.

The blanket 64 conventionally comprises, for example, a plurality oflayers of elastomer and fabric. The blanket 64 is fixed to the supportplate 62 by adhesive bonding or vulcanisation.

The front edge 66 of the support plate 62 extends beyond the front edge68 of the blanket 64. The front edge 66 of the support plate 62 is bentin the region of a front bend 70 in order to form with the rest of theplate 62 an acute angle β.

The front edge 68 of the blanket 64 is arranged in a slightly withdrawnposition relative to the bend 70. In some variants, however, the frontedge 68 can be in an advanced position in order to cover at leastpartially the bend 70. Be that as it may, the front edge 68 will belocated adjacent to the bend 70 in order not to extend into the aperture14.

The front edge 66 of the support plate 62 is not covered by the blanket64 and is inserted into the aperture 14. The front bend 70 extends overthe chamfer 18 and the front edge 66 of the plate 62 extends along thefront wall 16 of the aperture 14.

The blanket unit 3 has, at the rear, a configuration similar to the rearedge 72 of the plate 62, which edge 72 is not covered by the rear edge74 of the blanket 64. The rear edge 72 is bent in the region of a rearbend 76 relative to the rest of the support plate 62, forming an obtuseangle unlike the front of the blanket unit 3.

The bare rear edge 72 is inserted into the aperture 14 and extends alongand against the rear wall 20 of the aperture 14.

The rear edge 74 of the blanket 64 is arranged adjacent to the rear bend22 in order not to extend into the aperture 14 and to be relatively nearthe front edge 68 of the blanket 64.

The front edge 66 and rear edge 72 of the support plate 62 extend insidethe aperture 14 as far as the cavity 12 and together form an angle whichis not equal to zero.

As illustrated in FIG. 4, the rear edge 72 of the support plate 62 has,at the free end 78 thereof, a series of openings 80 distributed alongthe end 78. These openings 80 are substantially of rectangular form andare each arranged facing a pair comprising a hook 30 and pressingelement 32.

In order to mount the blanket unit 3 on the cylinder 2, the procedureis, for example, as follows,

The spindle 28 being in the release position, the front edge 66 of thesupport plate 62 is first inserted into the aperture 14, then theblanket unit 3 is wrapped around the cylinder 2 until the rear edge 72of the support plate 62 is engaged in the aperture 14. The blanket unit3 is then in the position of FIG. 2.

The spindle 28 is then pivoted, by means of the levers 56 and mechanisms42, from the release position thereof in FIG. 2, into the fixingposition thereof in FIG. 6.

During this rotation, the free end 34 of each hook 30 engages in thecorresponding opening 80 of the rear edge 72 of the support plate 62 andthe associated pressing element 32 extends through the same opening 80.This is illustrated in FIG. 5.

As the rotation movement of the spindle 28 continues, each hook 30 whichis firmly engaged against the periphery of the corresponding opening 80progressively brings about the tensioning of the support plate 2, whilstthe associated pressing element 32 which extends through the opening 80will press on the front edge 66 of the support plate 62 and press itagainst the front wall 16 of the aperture 14 and cavity 12.

It should be noted that each hook 30 applies a tension load T which issubstantially parallel with the rear edge 72 to the rear edge 72 of thesupport plate 62.

Once this movement is complete, the rear edge 72 of the plate 62 isdrawn by the hooks 30, thereby ensuring satisfactory tensioning of theblanket 64, and the front edge 66 of the support plate 2 is appliedagainst the front wall 16. It should be noted that the rear edge 72again forms an angle not equal to zero with the front edge 66 of thesupport plate 62.

In this manner, the blanket unit 3 is fixed to and tensioned on thecylinder 2 in a satisfactory manner.

In spite of this, the hooks 30 and the pressing elements 32 allow, owingto the construction thereof in the form of resilient elements, slightmovements of the edges 66 and 72 of the support plate 2. This allowsadaptation to various operating constraints of the offset printingmachine and, in particular, to the phenomenon of thermal expansion ofthe support plate 62 and the phenomenon known as “indention”.

In this manner, the rear edge 72 of the support plate 62 can, under theeffect of thermal expansion or in the case of the phenomenon known as“indention” extend further into the aperture 14, the hooks 30 allowingthis movement whilst keeping the blanket unit 3 under tension.

The pressing elements 32 form means 82 for applying the front edge 66 ofthe support plate 62 against the wall 16, which means 82 allow theblanket unit 3 to be stabilised on the cylinder 2.

Since these application means 82 are separate from the hooks 30, thestabilisation, fixing and tension of the blanket unit 3 are ensured in arelatively simple manner.

Furthermore, the use of the same openings 80 for receiving the hooks 30and the pressing elements 32 allows the number of openings in thesupport plate 62 to be limited.

It should also be noted that the use of openings 80 in the support plate62 for co-operating with the hooks 30 allows the support plate not tohave a curved rear edge, and therefore to keep the width l of theaperture 14 small. The inclination of the rear edge 72 of the supportplate 62 relative to the front edge 66 thereof also allows the aperture14 to have a small upstream width 1.

This width 1 is even smaller because neither the front edge 68 nor therear edge 74 of the blanket 64 extends into the aperture 14.

This allows the vibrations during the rotation of the various cylindersof the offset printing machine on each other to be greatly limited.

Since the blanket 64 further does not cover all the front edge 66 of thesupport plate 62, as in FR-2 573 347, the construction of the blanketunit and, in particular, the bending of the support plate are simple andeconomical, whilst limiting vibrations during operation.

In another embodiment illustrated in FIG. 8, the application means 82are formed, not by pressing elements 32 belonging to the fixing device26, but instead by a region of the rear edge 72 of the support plate 62.

In this manner, the rear edge 72 has an intermediate bend 84 whichdelimits, in the rear edge 72, an end region 86, in which the openings80 for receiving the hooks 30 are provided, and an intermediate region88 which is bent to a lesser extent relative to the rest of the supportplate 62. This intermediate region 88 presses on the front edge 66 ofthe support plate 62 and applies it against the wall 16.

FIG. 9 relates to a third embodiment which differs from that of FIGS. 1to 7 in that the means 82 for applying the front edge 66 of the supportplate 62 against the wall 16 have been dispensed with.

In spite of the absence of the application means 82, the fixing andtensioning of the blanket unit 3 have been found to be satisfactory.

It should be noted that, in the case of each of the above-describedembodiments, the cylinder and the blanket unit can be sold independentlyof each other.

In general, the above principles can be used with a cylinder 2, to whichtwo blanket units 3 are fixed, one beside the other, along axis A of thecylinder 2.

The fixing devices 42 associated with each blanket unit 3 can be offsetangularly from each other relative to axis A, for example, by 180°. Inthis manner, the apertures 14 associated with each blanket unit 3 arediametrically opposed, which limits the vibrations caused during therotation against the other cylinders of the printing machine, and do notextend over the entire length of the cylinder 2.

1. Assembly for an offset printing machine, comprising: a blanket unitcomprising a blanket and a blanket support plate, the front edge andrear edge of the support plate being bent over in the region of a frontbend and a rear bend, respectively, the rear edge of the support plateprotruding beyond the rear edge of the blanket which is located adjacentto the rear bend, and a cylinder having an aperture for receiving thefront edge and rear edge of the support plate, the cylinder comprising adevice for fixing the blanket unit to the cylinder, the fixing devicecomprising at least one hook for tensioning the blanket unit, the hookbeing intended to be received in one of at least one openings of therear edge of the support plate, which rear edge is inserted into theaperture, in order to apply to the support plate a tension load which issubstantially parallel with the rear edge thereof, the assembly furthercomprising, at least one element for pressing on the front edge of thesupport plate to apply the front edge of the support plate against thefront wall of the aperture, the pressing element belonging to the fixingdevice and being separate from the hook and the support plate, whereinthe pressing element extends, in order to press on the front edge of thesupport plate, through one of the at least one openings.
 2. Assemblyaccording to claim 1, wherein the opening is provided in a region of therear edge of the support plate forming an angle which is not equal tozero with the front edge of the support plate.
 3. Assembly according toclaim 1, wherein the hook comprises a resilient blade.
 4. Assemblyaccording to claim 1, wherein the pressing element comprises a resilientblade.
 5. Assembly according to claim 1, wherein the aperture has awidth, near the peripheral surface of the cylinder, of less than 1.5 mm.6. Assembly according to claim 5, wherein the width of the aperture isless than 1.1 mm.
 7. Assembly for an offset printing machine,comprising: a blanket unit comprising a blanket and a blanket supportplate, the front edge and rear edge of the support plate being bent overin the region of a front bend and a rear bend, respectively, the rearedge of the support plate protruding beyond the rear edge of the blanketwhich is located adjacent to the rear bend, and a cylinder having anaperture for receiving the front edge and rear edge of the supportplate, the cylinder comprising a device for fixing the blanket unit tothe cylinder, the fixing device comprising at least one hook fortensioning the blanket unit, the hook being intended to be received inan opening of the rear edge of the support plate, which rear edge isinserted into the aperture, in order to apply to the support plate atension load which is substantially parallel with the rear edge thereof,wherein the front edge of the support plate protrudes beyond the frontedge of the blanket which is located adjacent to the front bend, theassembly further comprising means for applying the front edge of thesupport plate against the front wall of the aperture, these applicationmeans being separate from the hook, and wherein the rear edge of thesupport plate is itself bent in the region of an intermediate bend whichdelimits an end region, in which the opening for receiving the hook isprovided, and an intermediate region which is intended to press againstthe front edge of the support plate and which thereby forms theapplication means.
 8. Assembly according to claim 7, wherein the openingis provided in a region of the rear edge of the support plate forming anangle which is not equal to zero with the front edge of the supportplate.
 9. Assembly according to claim 7, wherein the book comprises aresilient blade.
 10. Assembly according to claim 7, wherein the aperturehas a width, near the peripheral surface of the cylinder, of less than1.5 mm.
 11. Assembly according to claim 10, wherein the width of theaperture is less than 1.1 mm.
 12. Assembly for an offset printingmachine, comprising: a blanket unit comprising a blanket and a blanketsupport plate, the front edge and rear edge of the support elate beingbent over in the region of a front bend and a rear bend, respectively,the rear edge of the support plate protruding beyond the rear edge ofthe blanket which is located adjacent to the rear bend, and a cylinderhaving an aperture for receiving the front edge and rear edge of thesupport plate, the cylinder comprising a device for fixing the blanketunit to the cylinder, the flexing device comprising at least one hookfor tensioning the blanket unit, the hook being intended to be receivedin an opening of the rear edge of the support plate, which rear edge isinserted into the aperture, in order to apply to the support plate atension load which is substantially parallel with the rear edge thereof,wherein the front edge of the support plate protrudes beyond the frontedge of the blanket which is located adjacent to the front bend, andwherein the front wall and rear wall of the aperture form, starting fromthe peripheral surface of the cylinder, an angle which is less than 20°.13. Assembly according to claim 12, wherein the opening is provided in aregion of the rear edge of the support plate forming an angle which isnot equal to zero with the front edge of the support plate.
 14. Assemblyaccording to claim 12, wherein the hook comprises a resilient blade. 15.Assembly according to claim 12, wherein the aperture has a width, nearthe peripheral surface of the cylinder, of less than 1.5 mm. 16.Assembly according to claim 15, wherein the width of the aperture isless than 1.1 mm.
 17. Blanket unit for an offset printing machine, theblanket unit comprising a blanket and a blanket support plate, the frontedge and rear edge of the support plate being bent over in the region ofa front bend and a rear bend, respectively, the rear edge of the supportplate protruding beyond the rear edge of the blanket which is locatedadjacent to the rear bend, and the offset printing machine comprising acylinder having an aperture for receiving the front edge and rear edgeof the support plate, the cylinder comprising a device for fixing theblanket unit to the cylinder, the fixing device comprising at least onehook for tensioning the blanket unit, the hook being intended to bereceived in an opening of the rear edge of the support plate, which rearedge is inserted into the aperture, in order to apply to the supportplate a tension load which is substantially parallel with the rear edgethereof, wherein the rear edge of the support plate is bent in theregion of an intermediate bend which delimits an end region, in whichthe opening for receiving the hook is provided, and an intermediateregion which is intended to press against the front edge of the supportplate in order to apply the front edge of the support plate against thefront wall of the aperture.